Explanation

Weed pollen mix (allergy): what is measured?

The test measures, in one go, IgE antibodies against a fixed mix of pollen from 5 weeds that grow widely along roadsides, on wasteland and in gardens in the Netherlands: mugwort, ribwort plantain, fat hen (white goosefoot), European goldenrod and stinging nettle. IgE is the type of antibody that, in an allergic reaction, triggers mast cells to release histamine; the body only makes these antibodies after it has previously been in contact with an allergen, and this is called sensitization. Because the 5 weeds are tested together, the result gives one number and a verdict of positive or negative, but not which weed the antibodies are directed against. Ragweed (ambrosia) is not in the mix.

What can it detect?

Sensitization to weed pollen: the body has made IgE antibodies against pollen from at least one of the 5 weeds in the mix
An indication of whether symptoms of the nose, eyes or airways in summer and late summer may be caused by weed pollen

Result

What does the result mean?

Positive result

A positive result means that you have IgE antibodies against pollen from at least one of the weeds in the mix: sensitization. That is not the same as an allergy, and the test does not say which weed the antibodies are directed against. With symptoms such as sneezing, a blocked or runny nose, itchy or watery eyes or shortness of breath in summer and late summer, a positive result fits hay fever from weed pollen; according to the Longfonds (Dutch lung foundation), weeds such as mugwort and ragweed cause symptoms from July to September. In people without such symptoms, a positive result only means that the antibodies are there; no treatment follows.

Negative result

A negative result means that no IgE antibodies against pollen from the 5 weeds were found. Hay fever from these weeds is then much less likely. An allergy to ragweed is not tested with this mix. Symptoms in late summer can also come from grass pollen at the end of the season or from mold spores, and nasal symptoms can also have a non-allergic cause.

After an abnormal result

The GP mainly looks at the history: in which months and where the symptoms occur. With a positive result and matching symptoms, advice follows to reduce contact with pollen, such as keeping windows closed on dry, sunny days, and if needed medication for the nose and eyes. A test for single weed pollens can show which weed is involved; with a lot of symptoms despite medication, an allergist or ENT specialist can discuss immunotherapy.

Reliability

How reliable is the test?

A positive IgE result shows sensitization, not allergy: it only says that there are antibodies, not that you get symptoms from them. The Dutch medical specialists' guideline (FMS) on upper airway allergy recommends choosing an IgE test for single allergens based on the history of the symptoms; a mix tests more allergens at the same time, so a low sensitization without clinical meaning can more easily make the result positive. With weed pollen, the season overlaps with that of grasses in summer, so the season alone does not always say which allergen causes the symptoms. The mix is mainly a first step: a negative result makes hay fever from these weeds less likely, a positive result can be looked into further with a test for single weed pollens.

What can affect the result?

Sensitization without symptoms is common; the result can only be interpreted together with the history of the symptoms.
The test does not say which weed you react to; that requires a test for single weed pollens.
Ragweed and other weeds outside the mix are not measured, although antibodies against related weeds can cross-react.
Laboratories use different mixes, measurement methods and cut-off values; results from different labs cannot be compared one to one.

Who it is for

Who is the test useful for?

Useful for

Useful with symptoms of the nose, eyes or airways that come back every year in summer and late summer, into September, especially outdoors. If the symptoms already start in spring or occur mainly in May and June, a test for tree or grass pollen says more. In people without such symptoms, the test adds nothing: sensitization without symptoms is not a disease and is not treated.

How common is it?

Hay fever is common and often starts at a young age. Allergy to weed pollen is less common than allergy to grass or tree pollen; according to the Longfonds (Dutch lung foundation), weeds cause symptoms from July to September. Sensitization is more common than the allergy itself.

Longfonds; no Dutch prevalence figure has been checked

Drawbacks and risks

A positive result without symptoms can cause unnecessary worry or unnecessary measures, while sensitization without symptoms does not need treatment.
A negative result does not rule out symptoms in late summer from ragweed, grass pollen or molds.

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